The present invention relates to the technical field of treatment in the general sense by means of a heat transfer liquid, the treatment being applied to workpieces of any kind, and the method preferably relates to treating workpieces formed on a support on which components of the electronic, electrical, electro-mechanical, or mechanical type, for example, are mounted by means of a filler material that is deposited locally in association with component fixing tabs.
A particularly advantageous application of the invention lies in the treatment technique relating to assembling components by polymerization in which the filler material is constituted by a polymer, or in the component soldering or reflow technique in which the filler material is constituted by an alloy.
In the preferred technical field of the invention, various types of machine are known for fixing components on a support by melting a filler material. Thus, it is known to use a soldering machine for raising the temperature of the support and the components quickly and uniformly to a temperature which is slightly higher than the melting point of the filler material, thereby enabling bonding to be obtained by soldering or polymerizing the filler material.
In the state of the art, it is known to make a first category of machine in the form of a convection oven, an infrared oven, or a forced convection oven, optionally fitted with means for providing a controlled atmosphere. The main advantage of using an oven lies in the ease with which it can be inserted in a manufacturing line. Similarly, an oven makes it possible to treat workpieces on a continuous basis. Nevertheless, it must be understood that an oven presents major drawbacks associated essentially with relatively long treatment time, poor transmission of heat to the workpieces to be treated, high cost, and the use of an inert gas for ovens that operate under a controlled atmosphere.
A second category of machine is known in the state of the art that performs treatment by using the vapor of a heat transfer liquid. Thus, a vapor treatment machine generally comprises a vessel containing a liquid of the fluorocarbon type that is designed to be raised to a boiling temperature by heater means so as to produce a primary vapor that is saturated and inert in an assembly or bonding zone, with the temperature of the primary vapor being slightly higher than the melting point of the filler material The assembly or bonding zone extends substantially between the surface of the liquid and a heat exchanger coil for condensing the primary vapor. This assembly or bonding zone is optionally surmounted by a preheater zone or by a cooling zone occupied by a secondary vapor.
In its top portion, the vessel has a through opening that can be closed by a lid and that is designed to allow a support fitted with components that are to be assembled thereon to be inserted inside the vessel. Such a support is taken by a device which moves it and holds it successively in the preheating zone, in the bonding zone, and in the cooling zone. Thus, after the support has been held in the preheating zone for a determined length of time, it is brought into contact with the primary vapor to obtain a transfer of the latent heat of condensation of the vapor to the support and the associated components. This supply of heat raises the temperature of the support and the components quickly and uniformly to the temperature of the primary vapor, thereby causing the filler material to melt, and consequently, depending on the technique in use, causing the components to be bonded to the support by soldering or by polymerization.
That type of machine has undeniable advantages concerning the uniformity and the quality of heat transfer and it requires lower investment than that required for an oven. Nevertheless, that type of machine suffers from drawbacks concerning consumption of the heat transfer liquid and the difficultly of inserting the machine in a manufacturing line, and consequently of performing treatment on a continuous basis.
An investigation of previously known techniques leads to the observation that, at present, there exists no treatment machine which gives full satisfaction.
The object of the invention is to remedy that problem by proposing a method of applying heat treatment to a workpiece which is suitable for combining the advantages of the two known techniques while avoiding their drawbacks.
An object of the invention is thus to propose a method of applying heat treatment to a workpiece by means of a heat transfer liquid which enables the treatment operation to be integrated in a manufacturing line, thereby enabling treatment to be performed on a continuous basis, said method also providing heat transfer that is uniform and of good quality.
To achieve these objects, the invention thus provides a method of applying heat treatment to a workpiece by means of at least one heat transfer liquid having a boiling point at a given value, consisting in:
in placing the workpiece to be treated inside an oven whose internal structure defines a hermetic enclosure that is accessible via at least one door;
in placing the internal structure of the oven at a temperature that is suitable for enabling a fraction of a vapor obtained by vaporizing a heat transfer liquid to condense on the workpiece to be treated;
in causing the enclosure of the oven to be occupied by said vapor so as to ensure that a fraction of it condenses on the workpiece to be treated;
in extracting the vapor that remains in the oven enclosure; and
in extracting the workpiece from the oven.
The invention also provides a condensation oven for treating a workpiece, the oven comprising:
a case whose internal structure defines a hermetic enclosure that is accessible via at least one door;
heater means for heating the internal structure to a temperature suitable for enabling a fraction of vapor obtained by vaporizing a heat transfer liquid to condense on the workpiece to be treated;
a system for causing vapor obtained by vaporizing the liquid to occupy the inside of the enclosure, a fraction of which vapor is to condense on the workpiece to be treated; and
an extractor device for extracting the vapor occupying the inside of the hermetic enclosure of the oven.